In the usual fireplace structure, room air is drawn into the combustion chamber, and, after combustion, is passed up the chimney duct. Furthermore, after the fire in the chamber dies down, room air continues to pass through the chamber and up the duct. Both of these room air movements can cause large heat loss from the room. It would be beneficial to have a structure which does not depend upon room air for conbustion and which also prevents heat loss from the room after combustion in the structure has substantially ceased. The device of this invention achieves these desired results.